Use of a portable identifier with two communication protocols

Abstract

We propose a method for using a portable identifier configured to communicate with a vehicle system using a first communication protocol and a second communication protocol. The portable identifier includes an electrical power source. The method includes a determination S10 of the remaining energy level in the electrical power source. The method includes a measurement S20 of the temperature. The method includes a detection S30 that the determined remaining energy level is below a predetermined energy threshold and that the measured temperature is below a predetermined temperature threshold, followed by a change S40 in the communication from the first communication protocol to the second communication protocol. The second communication protocol is configured so that the voltage across the electrical power source remains above a predetermined voltage threshold.The process improves the use of the portable identifier. [Fig. 1].

Description

Title of the invention: Use of a portable identifier with two communication protocols technical field

[0001] This disclosure relates to a method of using a portable identifier communicating with a vehicle system, a computer program for such a portable identifier, a storage medium for such a program and a portable identifier for carrying out such a method. Technical background

[0002] Vehicles equipped with systems that have stored one or more portable identifiers now exist. These portable identifiers can be portable devices such as key fobs or smartphones. Each portable identifier includes a source of electrical power (for example, a battery) enabling it to be portable. Such systems allow the vehicle to perform functions, such as unlocking the doors and / or starting the vehicle, depending on the location of the portable identifier(s).

[0003] To perform these functions, each wearable device can be configured to communicate with the system using a UWB (Ultra Wide Band) communication protocol. This protocol can, in particular, allow the wearable device to be located around the vehicle through several successive UWB exchanges between system anchors and the wearable device. However, these UWB exchanges consume a significant amount of energy, which can lead to location failures when the available energy in the device is insufficient.

[0004] There is therefore a need to improve the use of these portable identifiers and in particular their ability to be located by the system. Summary

[0005] A method is proposed for this purpose of using a portable identifier configured to communicate with a vehicle system using a first communication protocol and a second communication protocol. The portable identifier includes an electrical power source. The method includes determining the remaining energy level in the electrical power source. The method includes measuring the temperature. The method includes detecting that the determined remaining energy level is below a predetermined energy threshold and that the measured temperature is below a predetermined temperature threshold. The method includes, After detection, the communication protocol changes from the first to the second. The second protocol is configured to ensure that the voltage across the electrical power source remains above a predetermined threshold.

[0006] The communication may include successive localizations of the wearable identifier relative to the vehicle. Each localization may include UWB exchanges between the wearable identifier and the vehicle system. The localizations may be performed, after modification, using the second communication protocol.

[0007] Locations performed using the second communication protocol may include fewer UWB exchanges than locations performed using the first communication protocol.

[0008] The vehicle system may include anchors. The UWB exchanges of each location may include receptions by the portable identifier of signals sent by the system anchors. The number of signals received from each location implemented using the second communication protocol may be less than the number of signals received from each location implemented using the first communication protocol.

[0009] The time spacing between UWB exchanges of locations made using the second communication protocol may be greater than the time spacing between UWB exchanges of locations made using the first communication protocol.

[0010] The UWB exchanges of each location may include signal emissions via the portable identifier to the system. The transmission power of the second protocol may be lower than the transmission power of the first communication protocol.

[0011] The portable identifier and / or the system may further include a memory on which a calibration table is stored. The calibration table may include communication protocol parameters to be applied based on temperature and energy thresholds. The method may include determining the parameters of the second communication protocol by reading the calibration table.

[0012] The temperature measurement step can be carried out by the handheld identifier or by the vehicle system.

[0013] A computer program for such a portable identifier is also proposed. The computer program includes instructions which, when the program is executed by a processor of the portable identifier, cause the latter to implement such a process.

[0014] A computer-readable storage medium is also proposed on which such a computer program is recorded.

[0015] A portable identifier is also proposed. The portable identifier includes such a storage medium. The portable identifier is configured to perform such a process. Brief description of the figures

[0016] Non-limiting examples will be described with reference to the following figures:

[0017] [Fig.1] shows an example of a process flowchart.

[0018] Figure 2 illustrates an example of a vehicle and portable identifier system.

[0019] Figures [Fig.3] and [Fig.4] illustrate an example of a portable identifier.

[0020] Figure 5 illustrates an example of localization between a vehicle system and a portable identifier.

[0021] Figures [Fig. 6] and [Fig. 7] illustrate examples of results.

[0022] Figures [Fig.8], [Fig.9] and [Fig.10] illustrate examples of localizations carried out using the second communication protocol.

[0023] Fig. 11 shows an example of a calibration table.

[0024] Figures [Fig.12] and [Fig.13] illustrate examples of portable identifier architecture. Detailed description

[0025] With reference to the flowchart in [Fig. 1], a method is proposed for using a portable identifier configured to communicate with a vehicle system using a first communication protocol and a second communication protocol. The portable identifier includes an electrical power source. The method includes a determination S10 of the remaining energy level in the electrical power source. The method includes a measurement S20 of the temperature. The method includes a detection S30 that the determined remaining energy level is below a predetermined energy threshold and that the measured temperature is below a predetermined temperature threshold. The method includes, after the detection S30, a change S40 in the communication from the first communication protocol to the second communication protocol.The second communication protocol is configured so that the voltage across the electrical power source remains above a predetermined voltage threshold.

[0026] The method improves the use of the portable identifier.

[0027] Indeed, the method reduces the risk of communication interruption between the wearable identifier and the system. Such an interruption can occur, in particular, when the temperature is low and the energy level available in the wearable identifier becomes insufficient. In such a situation, the wearable identifier's energy storage capacity may be insufficient to perform several successive UWB exchanges between the system and the wearable identifier, such as during a localization operation. of the wearable identifier. When this is likely to happen, the process modifies the communication to use a second communication protocol in which the voltage across the electrical power source remains above a predetermined voltage threshold. With this second protocol, all successive UWB exchanges are therefore feasible, despite the low temperature and low energy level. The process thus maintains communication between the wearable identifier and the system, preventing disruptions, such as a loss of the wearable identifier's location, which could otherwise occur.

[0028] In particular, the method takes into account both the remaining energy level and the measured temperature, which improves the detection of a risky situation. Indeed, a low energy level is particularly problematic when the temperature drops. The method therefore ensures that the switch from the first to the second protocol only occurs when there is a real risk of failure. In other words, the method maintains communication as much as possible using the first (more comprehensive) protocol, and only switches to the second (more limited) protocol in the event of a real risk of failure. In other words, the method dynamically adjusts the communication protocol used according to the remaining energy level, ultimately improving the overall quality of the communication.

[0029] The method of use can be executed while UWB communication is in progress between the wearable identifier and the vehicle system. The wearable identifier and the system can, for example, communicate when the wearable identifier is within a certain perimeter around the vehicle, for example when the user wearing the wearable identifier is inside the vehicle, or when approaching or moving away from it.

[0030] Such UWB communication may include successive localizations, for example, at certain intervals, of the wearable identifier relative to the vehicle. Each of these localizations may include UWB exchanges between the wearable identifier and the vehicle system. Initially, that is, before the execution of steps S10 to S40, the communication protocol used is the first communication protocol. The localizations are therefore performed using the first communication protocol. After the execution of steps S10 to S40, the communication is modified, and the communication protocol used becomes the second communication protocol. The localizations are therefore performed using this second communication protocol.

[0031] The method of use may include determining the position of the portable identifier from the location operations that were performed during the communication. For example, performing a location operation may include a Providing a relative position of the wearable identifier with respect to the UWB system. In particular, each location can include UWB exchanges between the wearable identifier and several UWB anchors (also called "sensors") of the system (for example, all anchors) to determine the respective distances between the wearable identifier and each of the anchors. Each location can then include a determination of the relative position of the wearable identifier with respect to the UWB system based on the determined distances (the position corresponding, for example, to the intersection of circles drawn from the anchors and having diameters equal to the calculated distances).

[0032] Each distance to an anchor can be measured by exchanging a UWB signal between the identifier and the anchor and calculating a time-of-flight between the identifier and the anchor during this exchange. This time-of-flight can be the time taken by the exchanged signal to travel to and from the identifier and the anchor. The time-of-flight can be calculated by either the identifier or the anchor, and can be performed in any way. For example, each measurement can include recordings of the times the exchanged signal is sent and received, and the calculation can be performed by subtracting the time taken by the signal to travel to and from the anchor from these recordings. Each measurement can then include subtracting the distance between the identifier and the anchor from this time-of-flight. For example, each measurement can include multiplying a signal velocity by the calculated time-of-flight.The signal speed can, for example, be a predetermined and known speed for this type of signal (for example, stored in the identifier or system memory).

[0033] Successive localizations performed during communication can allow the position of the portable identifier to be determined in real time. For example, each localization can provide a position of the portable identifier relative to the UWB system at a given instant, and the set of all performed localizations can provide an evolution of its position over time. The method of use can thus include determining the evolution of the portable identifier's position from successive localizations performed using the first or second communication protocol.

[0034] The method of use may also include one or more uses of the determined relative positions of the portable identifier. For example, the method of use may include activating one or more vehicle features depending on the position of the portable identifier. For example, the feature may include locking the vehicle when it is determined that the portable identifier is outside the vehicle, for example, after a predetermined time has elapsed between the time it is determined that the portable identifier is outside. In some examples, the feature may include a Selective unlocking of one or more vehicle doors (e.g., a driver's door, a passenger's door, or the trunk) based on the relative positions of the wearable device. For example, the functionality might include unlocking the driver's door or the trunk when the wearable device approaches the door or trunk. In other examples, the functionality might include activating one or more vehicle functions, such as turning on the music or adjusting the mirrors to suit the person wearing the wearable device, which is positioned near the driver's seat. The method of use could include any combination of these functionality examples.

[0035] Each step of the process is now discussed in more detail.

[0036] The step S10 of determining the remaining energy level can be performed by The portable identifier. In one example, the S10 determination of the energy level might involve measuring the battery's open-circuit voltage and its charging voltage, then calculating the internal resistance of the energy source (e.g., the battery) from the difference between these two voltages (e.g., using the formula U = Er*I, thus calculating r = (EU) / I, where E is the open-circuit voltage, U is the charging voltage, r is the internal resistance, and I is the charging current). The S10 determination of the energy level might then involve deducing the remaining energy level based on the calculated internal resistance value. Alternatively, in a second example, the portable identifier might include an electronic component configured to measure the remaining energy level in the electrical energy source, such as a voltage converter (also called a "voltage booster").Such a component can, for example, be configured to supply the amount of energy (e.g., the number of mAh) that has been consumed from the electrical power source. The remaining energy level can then be deduced from this amount of energy consumed, for example, by subtracting this amount of energy consumed from the total energy available in the power source before consumption.

[0037] The temperature measurement step S20 can be performed by the wearable identifier. The wearable identifier may include an electronic component configured to measure the temperature experienced by the wearable identifier, either by the UWB component or the BLE component, or by adding a temperature sensor. The measurement step S20 may include a temperature measurement by this sensor. Alternatively, this step can be performed by the vehicle system, for example with a temperature sensor located in the vehicle.

[0038] The detection step S30 determines that the remaining energy level is below the predetermined energy threshold, and that the measured temperature is below the threshold of A predetermined temperature can be set while the steps S10 for determining the remaining energy level and S10 for measuring the temperature are performed. These steps can be carried out continuously, for example at a specific frequency (same or different), so as to provide the remaining energy level and the temperature at each instant. With each new measurement of temperature or remaining energy level, the process can include a comparison of the new measurement with the corresponding threshold (energy threshold for the remaining energy level and temperature threshold for the measured temperature).The process can then detect S30 that the determined remaining energy level is below a predetermined energy threshold and that the measured temperature is below a predetermined temperature threshold when the comparison indicates that the new measured values ​​fall below the predetermined thresholds.

[0039] The energy threshold can represent a minimum amount of energy remaining in the energy source. For example, the energy threshold can be expressed as a percentage of the maximum amount of energy that can be stored in the energy source, and can represent a minimum percentage of remaining energy, for example, between 50 and 75%. In this case, the determined remaining energy can also be expressed as a percentage, for example, of the maximum energy of the energy source. The temperature threshold can represent a minimum temperature that must not be exceeded. The temperature threshold can, for example, be between 10 and -10°C. The temperature threshold can, for example, be equal to 0°C.

[0040] The detection step S30, which determines that the remaining energy level is below the predetermined energy threshold and that the measured temperature is below the predetermined temperature threshold, can be performed by the handheld device. In this case, the handheld device can be configured to record the measured remaining energy level and temperature values ​​(e.g., continuously), for example, in memory. The handheld device can then be configured to compare these values ​​with the predetermined energy and temperature thresholds. Alternatively, the detection step S30 can be performed by the vehicle system. In this case, the handheld device can be configured to send the measured remaining energy level and temperature values ​​to the vehicle system, which can then be configured to compare them with the predetermined thresholds (after, for example, recording them in the vehicle's memory).

[0041] The modification step S40 is performed immediately after the detection step S30. In other words, when it is detected that the determined remaining energy level is below the predetermined energy threshold and that the measured temperature is below the predetermined temperature threshold, the modification to the second protocol occurs. is performed. UWB localization between the system and the wearable device can then be performed using this second protocol. The S40 modification can be performed by the wearable device and / or the system. The S40 modification may involve the wearable device sending a signal to the system, including, for example, the measured temperature and / or the remaining energy level. The S40 modification may then involve receiving the signal sent by the system and selecting the second protocol to be implemented by the system, for example, based on the measured temperature and / or the remaining energy level. The system may, for example, include memory on which a calibration table is stored. This calibration table may include communication protocol parameters to be applied based on temperature and energy thresholds.For example, each row in the table might include a respective range for temperature and energy level values ​​and associated protocol parameters. The reading process might involve identifying the corresponding row based on the measured values ​​and deducing the parameters to be used. In this case, the process might include determining the parameters of the second communication protocol by reading the calibration table. This second protocol can then be sent to the portable identifier for use.

[0042] Alternatively, the portable identifier can be configured to propose a second protocol to the system. In this case, the portable identifier can include memory on which the previously discussed calibration table is stored. The portable identifier can be configured to determine the parameters of the second communication protocol to be used by reading this calibration table (in the same way as the system, for example). The signal sent by the portable identifier can then include the parameters of this second protocol as determined. Modification S40 can then include validation of this proposal by the system, and the sending, for example, of a validation message for the new proposed protocol to the portable identifier. Alternatively, both the system and the portable identifier can have the table available, and one can, for example, thus verify the solution proposed by the other.

[0043] The second communication protocol is configured so that the voltage across the electrical power source remains above a predetermined voltage threshold. This means that the parameters of this protocol allow the battery voltage to remain above this voltage threshold, particularly during each location sequence performed with the vehicle's UWB system. The remaining energy in the power source is sufficient to allow each location sequence to be performed without the voltage falling below the predetermined voltage threshold.

[0044] In a first implementation example, the second protocol can reduce the number of UWB exchanges performed at each location. For example, in the first protocol, each location may include distance measurements with all the anchors in the system, whereas in the second protocol, each location may include measurements with a smaller number of anchors (for example, a minimum of two), thus reducing the number of exchanges performed and therefore the energy used. Each distance measurement with an anchor may include the transmission of a signal by the anchor to the portable identifier, and therefore the reception of this signal by the portable identifier.In the first protocol, the wearable device can receive signals sent by all system anchors, while in the second protocol, the wearable device can listen to only a limited number of system anchors (for example, at least two), and therefore only receive signals from this limited number of anchors. The anchors listened to can be selected by the wearable device or the system, and may or may not vary with each location measurement. For example, the system can suggest anchors to the wearable device based on its position, such as the one measured during the last location measurement. The suggested anchors might, for example, be those furthest away on either side of the vehicle relative to the wearable device's position, thus maintaining better measurement accuracy.

[0045] In a second implementation example, the second protocol can increase the time spacing between UWB exchanges for each location. For example, each location might include successive signal exchanges between the handheld identifier and several system anchors (e.g., all anchors), and the signal exchanges might be more spaced out in the second communication protocol than in the first. The time spacing between exchanges might correspond to the time interval between two successive exchanges, that is, between the end time of the first and the start time of the second. The time spacing between all exchanges for the location might be greater than a first duration in the first protocol, and greater than a second duration in the second protocol, and the first duration might be less than the second duration.The time interval between all location exchanges can be greater than or equal to 4000ps in the second protocol, for example. This allows for greater spacing of the energy used, and therefore allows the voltage in the energy source to rise between the different exchanges, and thus remain above the predetermined voltage threshold.

[0046] In a third implementation example, the second protocol can reduce the signal transmission power of the wearable identifier. At each location, the wearable identifier can send signals to the system and to each anchor of the system, for example, to perform distance measurements. In the first In the first protocol, signals sent by the wearable identifier can be sent with a first power level, and in the second protocol, signals can be sent with a second power level lower than the first. This allows less energy to be used for each signal sent, and therefore allows the voltage to remain above the predetermined voltage threshold.

[0047] In examples, the method can combine any of the first, second, and third implementation examples discussed previously. For example, the second protocol can both reduce the number of UWB exchanges (as in the first implementation example) and increase the time spacing between this reduced number of UWB exchanges (as in the second implementation example). Alternatively, the second protocol can both reduce the number of UWB exchanges (as in the first implementation example) and reduce the power of the transmitted signals (as in the third implementation example). Alternatively, the second protocol can both increase the time spacing between UWB exchanges (as in the second implementation example) and reduce the power of the transmitted signals (as in the third implementation example).Alternatively, the second protocol can both reduce the number of UWB exchanges (as in the first implementation example), increase the time spacing between this reduced number of UWB exchanges (as in the second implementation example), and reduce the power of the signals sent (as in the third implementation example).

[0048] In some examples, the vehicle system may have stored several wearable identifiers. In this case, when a user wearing one of these wearable identifiers approaches the vehicle, the steps of the process can be executed for that identifier. When another of the wearable identifiers approaches the vehicle (for example, when worn by the same user or by another user), the process can be repeated for that other identifier.

[0049] UWB communication can continue, for example, until the user enters the vehicle or starts the vehicle (e.g., starts the vehicle's engine). At that point, UWB communication may vary. For example, when the user enters the vehicle or starts the vehicle, the frequency of location updates may decrease.

[0050] The electrical power source can be a battery. For example, the electrical power source can be a button cell. The battery can have a large electrical capacity, for example, a capacity greater than 320 mAh. The battery can, for example, have an electrical capacity of 620 mAh. The battery can be, for example, a CR2450 button cell.

[0051] Examples will now be described with reference to Figures 2 to 13.

[0052] Figure 2 illustrates an example of a vehicle system 100 and a portable identifier 200. The system includes anchors 111, 112, 113, 114, 115 and 116 positioned at different locations on the vehicle 100. The portable identifier 200 is in this example a key fob.

[0053] The wearable device and the system are configured to communicate with each other, specifically to locate the wearable device 200 around the vehicle 100. The communication between the wearable device 200 and the vehicle system includes successive UWB localizations of the wearable device 200 around the vehicle 100 in order to calculate in real time the position of the wearable device 200 around the vehicle 100. Each UWB localization includes UWB exchanges between the wearable device 200 and the system anchors 111, 112, 113, 114, 115, and 116 in order to determine the respective distances between the wearable device 200 and each of the anchors 111, 112, 113, 114, 115, and 116. Each localization then includes a determination of the relative position of the wearable device 200 with respect to the UWB system. distances determined with each anchor 111, 112, 113, 114, 115 and 116.

[0054] Each distance to an anchor is measured by exchanging a UWB signal between the identifier and the anchor and calculating a time-of-flight between the identifier and the anchor during these exchanges. This time-of-flight can be the time taken by the exchanged signal to travel to and from the identifier and the anchor. The time-of-flight can be calculated by the identifier and can be performed in any way. For example, each measurement can include recordings of the times the exchanged signal is sent and received, and the calculation can be done by subtracting the time taken by the signal to travel to and from the anchor from these recordings. Each measurement can then include subtracting the distance between the identifier and the anchor from this time-of-flight.The flight times can then be sent to all anchors (for example, by sending the same frame with all the flight times), and each anchor can calculate the position of the identifier relative to itself using the sent flight times. For example, each measurement could involve multiplying a signal velocity by the calculated flight time. The signal velocity could, for example, be a predetermined and known velocity for that type of signal (for example, stored in the identifier's or system's memory). All this information can then be sent to the main computer, which can deduce the exact position of the identifier (relative to the center of the vehicle).

[0055] Figure 3 shows an example of a housing with a width of 45 mm and a length of 77 mm. Figure 4 illustrates an example of a portable identifier printed circuit board, and in particular the two sides 201, 202 of this circuit. Such a circuit can be located inside the housing illustrated in Figure 3. The circuit includes antennas 230, 270, 260, a 240 battery, and six 250 buttons. During each localization operation, energy is drawn from a reservoir capacitance composed of several capacitors 210. Since the dimensions of a handheld identifier are limited, the space available for these capacitors 210 is restricted, thus reducing the achievable reservoir capacitance. Therefore, it is not possible to solve the problem of localization failures by increasing the reservoir capacitance of the housing. For example, to achieve a reservoir capacitance of 430 pF with SMD capacitors each having a maximum capacitance of 47 pF, more than 10 capacitors would be required (accounting for 25% degradation). However, this is impossible due to the housing dimensions. The housing dimensions can, for example, range from 20 to 40 mm in width and 40 to 70 mm in length. The handheld identifier can contain a maximum of 2 to 5 capacitors.This can represent a reservoir capacitance between 125 pF and 350 pF, for example, between 150 pF and 250 pF. The reservoir capacitance could, for example, be 164 pF or 250 pF. The portable identifier can only contain a maximum of 5 capacitors, and it is not possible to add more without increasing the size of the PCB, and therefore the package. This method overcomes this problem by reducing the risk of localization failure without increasing the package size.

[0056] Figure 5 illustrates an example of communication between the vehicle system 100 and the portable identifier 200 of Figure 2. The communication comprises successive UWB locations 401, 402 between the vehicle system 100 and the portable identifier 200. The successive UWB locations 401, 402 are performed in this figure using the first communication protocol.

[0057] Each localization operation includes UWB 410, 420, and 430 exchanges to determine the respective distances between the portable identifier and the UWB anchors of the system, and to determine the relative position of the portable identifier with respect to the UWB system based on these distances. In particular, the localization operation includes two 410 transmissions of a frame on the first two 410 time slots from the UWB portable identifier to each of the UWB anchors of the system. The localization operation then includes, successively and on a respective time slot, the transmission of a 420 frame by each of the UWB anchors (in this example, the system comprises 6 anchors, and 6 frames are therefore received by the portable identifier). The localization operation then includes two 430 transmissions of a frame on the last two time slots from the UWB portable identifier to each of the UWB anchors of the system.

[0058] Figures 6 and 7 illustrate examples of results. In particular, Figure 6 shows tables listing the localization failures when the usage procedure is not used, i.e., when the localizations are performed according to the first protocol only. Table 510 shows the results obtained when the energy source is full, and Table 520 shows the results obtained when the source The energy source is discharged to 50%, and the table shows the results obtained when the energy source is discharged to 80%. The results show that when the energy source is full, there are no localization failures ("PASS" for all temperatures in Table 510). However, when the energy source is discharged to 50%, localization fails when the temperature drops below 0°C ("KO" for the 0°C, -10°C, and -20°C temperature ranges in Table 520). When the energy source is discharged to 80% (Table 530), the results show that localization fails at -10°C when the reservoir capacity is 250 pF, at 0°C when the reservoir capacity is 164 pF, and at 20°C when the reservoir capacity is 100 pF.

[0059] Figure 7 illustrates an example of these localization failures when using the first communication protocol at low temperatures and with low remaining energy. In particular, the figure shows the evolution of the voltage across the energy source during localization. The evolution shows that initially the voltage is sufficient, but that it decreases with each exchange, and that after the 7th exchange, it falls below 1.8V, resulting in a localization failure (as the last exchanges are not completed).

[0060] The method makes it possible to avoid such localization failures, by changing the communication to the second communication protocol when the temperature is low and the remaining energy is low so that the voltage across the terminals of the electrical energy source remains above 1.8V so that the localizations do not fail.

[0061] Figures [Fig.8], [Fig.9] and [Fig.10] illustrate examples of localizations carried out using the second communication protocol.

[0062] In particular, [Fig. 8] shows the first implementation example in which the second protocol reduces the number of UWB exchanges performed at each localization. In this example, each localization performed in the second protocol includes measurements with a smaller number of anchors (e.g., two in this example), which reduces the number of exchanges performed, and therefore the energy used. As in the first protocol, localization initially comprises two transmissions of a frame on the first two time slots from the UWB portable identifier to each of the UWB anchors of the system. Localization then comprises, successively and on a respective time slot, a reception of frames sent by the UWB anchors. In the first protocol, the portable identifier can receive signals sent by all the anchors of the system (as illustrated in [Fig. 5]).In the second protocol, however, the portable identifier listens to only a limited number of anchors (two in this example), and therefore only receives signals from these two anchors, 621 and 622. The anchors listened to can vary. For example, in the first example, the first two 621 anchors are listened to, while in the second, the first 621 anchors are listened to. and fourth anchors 622 are listened to. The localization then includes two 630 transmissions of a frame on the last two time slots from the UWB portable identifier to each of the UWB anchors of the system.

[0063] Figure 9 shows the evolution of the voltage across the power source when localization is performed in the second communication protocol as illustrated in Figure 8. The figure shows that the voltage remains above the 1.8V 640 threshold. Indeed, since fewer exchanges are performed, and they are more spaced out, the voltage no longer falls below this threshold.

[0064] Figure 10 illustrates the second implementation example in which the second protocol increases the time spacing between the UWB exchanges of each location. In this second example, the signal exchanges performed during each location are more spaced out in the second communication protocol than in the first. This allows for greater spacing of the energy used, and therefore allows the voltage in the energy source to rise between the different exchanges, and thus remain above the predetermined voltage threshold. The time spacing between the UWB exchanges of a location is illustrated in Figure 8 and is designated by reference 610. Figure 10 shows, in particular, the evolution of the voltage across the energy source when the time spacing is not increased (2660 ps), and those obtained for increases in time spacing of 4000 ps, ​​5000 ps, ​​and 7000 ps.The results show that the voltage across the power source remains above the voltage threshold of 1.8V when the time interval is at least 4000ps.

[0065] Figure 11 shows an example of a calibration table. Such a table can be stored in memory at the handheld device or system level and can be used to select the parameters of the second protocol to be implemented based on the measured temperature and / or the remaining energy level. The calibration table includes communication protocol parameters to be applied according to temperature and energy thresholds. In particular, the calibration table includes rows corresponding to different situations and columns indicating, for each situation, the corresponding temperature and remaining energy thresholds 720, 730, and the parameters to be applied, namely the maximum number of anchors to listen to 730, the minimum time spacing to be applied 750, and / or the maximum transmission power to be used 760 for the second communication protocol.The parameter selection process may therefore involve identifying the table row corresponding to the current situation using the indicated temperature and discharge thresholds, and then deducing the parameters to be applied by reading the parameters indicated for the identified row. The table may also include a first column 710 indicating the voltages of the corresponding energy source. to the different discharges of column 720. Thanks to this first column 710, it is possible to directly deduce the corresponding discharge as a function of the measured voltage (this value being more easily measurable).

[0066] Figure 12 illustrates a first example of the 801 architecture of the portable identifier. The 800 architecture includes a UWB component 810 and a BLE component 820. The 800 architecture includes a UWB antenna 811 connected to the UWB component 810. The 800 architecture includes a BLE antenna 821 connected to the BLE component 820. The 800 architecture includes a battery 850 powering the UWB component 810 and the BLE component 820. In this first example, the energy level can be determined by calculating the internal resistance of the battery 850 from measurements of the open-circuit and load voltages, to deduce the remaining energy level as explained previously. Figure 12 illustrates the 801 architecture of the portable identifier. 13] illustrates a second example of 802 architecture. In this second example, the portable identifier also includes an 840 voltage converter (also called a "voltage booster"), which is configured to measure the remaining energy level in the 850 battery.For example, this component can be configured to provide the amount of energy (e.g., the number of mAh) that has been consumed from the power source. In this second example, the remaining energy level can therefore be deduced from this amount of energy consumed. Alternatively, the remaining energy level can be deduced by calculating the internal resistance of the 850 battery, as in the first example.

Claims

Demands

1. A method of using a portable identifier configured to communicate with a vehicle system using a first communication protocol and a second communication protocol, the portable identifier comprising an electrical power source, the method comprising: • a determination (S10) of the remaining energy level in the electrical power source; • a measurement (S20) of the temperature; • a detection (S30) that the determined remaining energy level is below a predetermined energy threshold and that the measured temperature is below a predetermined temperature threshold; and • after the detection (S30), a change (S40) of the communication from the first communication protocol to the second communication protocol, the second communication protocol being configured so that the voltage across the electrical power source remains above a predetermined voltage threshold.

2. A method according to claim 1, wherein the communication comprises successive localizations of the wearable identifier relative to the vehicle, each localization comprising UWB exchanges between the wearable identifier and the vehicle system, the localizations being carried out, after modification, using the second communication protocol.

3. A method according to claim 2, wherein the localizations performed using the second communication protocol include fewer UWB exchanges than the localizations performed using the first communication protocol.

4. A method according to claim 3, wherein the vehicle system includes anchors, the UWB exchanges of each location comprising receptions by the portable identifier of signals sent by the anchors of the system, the number of signals received from each location realized using the second communication protocol being less than the number of signals received from each location realized using the first communication protocol.

5. A method according to any one of claims 2 to 4, wherein the time spacing between UWB exchanges of locations made using the second communication protocol is greater than the time spacing between UWB exchanges of locations made using the first communication protocol.

6. A method according to any one of claims 2 to 5, wherein the UWB exchanges of each location include signal emissions by the portable identifier to the system, the power of the emissions of the second protocol being less than the power of the emissions of the first communication protocol.

7. A method according to any one of claims 2 to 6, wherein the portable identifier and / or the system further comprise a memory on which a calibration table is recorded, the calibration table comprising communication protocol parameters to be applied as a function of temperature and energy thresholds, the method comprising a determination of the parameters of the second communication protocol by reading the calibration table.

8. A method according to any one of claims 2 to 7, wherein the temperature measurement step (S20) is carried out by the handheld identifier or by the vehicle system.

9. A portable identifier computer program comprising instructions which, when the program is executed by a processor, cause the processor to implement the method according to any one of claims 1 to 8.

10. Computer-readable storage medium on which the computer program according to claim 9 is recorded.

11. Portable identifier comprising the storage medium according to claim 10, the portable identifier being configured to perform the method according to any one of claims 1 to 8.

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